Search

Highlights • Integrated Tonian & Cambrian stratigraphy in Huaibei region at the southeastern (SE) margin of the North China Craton (NCC). • The Great Unconformity is identified and positioned between the redefined Tonian Gouhou Formation and the Cambrian Houjiashan Formation at the SE margin of the NCC. • The Great Unconformity at the SE margin of the NCC represent a ca. 200–300 Myr gap. • New data provide insights into Tonian-Cambrian tectonic history in the NCC. Abstract The Great Unconformity between the Precambrian basement rock and Cambrian sedimentary cover has been extensively documented in Laurentia and may provide insights into the environmental context of the Cambrian explosion. A similar unconformity has been known in the North China Craton (NCC) and it offers an opportunity to constrain the geographic extent and geochronological magnitude of the Great Unconformity. However, the placement and magnitude of the Great Unconformity in the NCC, particularly at the southeastern margin of the NCC, is uncertain. For example, in the Huaibei region of the southeastern margin of the NCC, this unconformity has been variously placed beneath or above the Gouhou Formation, which preserves critical micro- and macrofossil assemblages with great paleobiological and biostratigraphic significance. This uncertainty significantly hampers our ability to fully appreciate the geological history of the NCC. To resolve this issue, we carried out an integrated biostratigraphic, sedimentary petrological and detrital zircon geochronological investigation on the Gouhou Formation and the overlying Houjiashan Formation in the Huaibei region. Our data suggest that the Great Unconformity lies within the Gouhou Formation and represents a ca. 200–300 Myr depositional gap: the Lower Member of the Gouhou Formation is of Tonian age whereas the Middle-Upper members of the Gouhou Formation are of early Cambrian. Therefore, we propose that the Gouhou Formation be redefined to contain only the Lower Member, and the Middle-Upper members be included in the Houjiashan Formation. Our analysis also confirms that the Great Unconformity can be widely recognized along the southeastern margin of the NCC. The recognition of the Great Unconformity in the Huaibei region helps to clarify the tectonic history, basin development, stratigraphic correlation, and paleogeographic reconstruction of the southeastern margin of the NCC during the Tonian–Cambrian periods. [ABSTRACT FROM AUTHOR]

Orbisiana is an Ediacaran fossil characterized by linearly arranged circular or cylindrical units. The genus was first described from the late Ediacaran Redkino Series in the Moscow Syncline of Russia where it is preserved as pyritic molds in siltstone. Here we report Orbisiana linearis , originally described as Seirisphaera lineare , from black shale of the early Ediacaran Lantian Formation in South China. Unlike the type species ( O. simplex ), O. linearis is preserved as carbonaceous compressions on the bedding surface, with rare specimens preserved three-dimensionally, allowing morphological characterization using X-ray microCT techniques. Morphological, paleoecological and taphonomic analysis suggests that O. linearis was a chain-like modular organism characterized by uniserially arranged, millimeter-sized, and tangentially contacting circular or cylindrical units. Ontogenetic growth of O. linearis was likely achieved through both accretionary addition of new modules and inflational expansion of existing units, and it appears that inflational growth was determinate. Although its phylogenetic affinity remains uncertain, O. linearis was likely a procumbent epibenthic or semi-endobenthic organism that lived on the seawater-sediment interface or partly buried in sediments. O. linearis in the Lantian Formation was preserved in situ, although some specimens are disarticulated and many are tectonically deformed. Orbisiana joins a growing list of Ediacaran genera that have a remarkable range of stratigraphic, environmental, ecological, and taphonomic distribution. [ABSTRACT FROM AUTHOR]

• Source magma of K-bentonite in Doushantuo cap dolostone at Jiuqunao is rhyodacitic. • Source magma of K-bentonite in Doushantuo cap dolostone at Heyu is pantelleritic. • Two episode K-bentonites in Doushantuo cap dolostone have been identified. • K-bentonites have potential significance to the genesis of Marinoan cap dolostone. A study of the K-bentonites in the Doushantuo cap dolostones on the Yangtze Platform in South China would facilitate understanding the origin of the Marinoan cap dolostones and testing the snowball Earth hypothesis. To date, sporadic work has been conducted on the whole-rock geochemistry of the K-bentonites from the platform and slope of the Yangtze Platform, to preliminarily understand the genesis of the K-bentonites. However, a study of the whole-rock geochemistry of the K-bentonites from the basin and on zircon geochemistry of the K-bentonites from the entire Yangtze Platform has not been carried out. Therefore, the nature of the primary magmas, source and tectonic setting of the source volcanoes, and the episodes of source volcanic eruptions of the K-bentonites are unknown, which hinders unraveling the possible link between the sedimentary model of the Marinoan cap dolostone and the K-bentonites. Here, we perform a systematic study of the whole-rock and zircon geochemistry of the K-bentonites. The major and trace element concentrations of the K-bentonites and trace element contents in their volcanic zircons suggest that the primary magmas of the K-bentonites from the Jiuqunao and Heyu sections are different in nature. The same geochemical results indicate that the source volcanoes of all the K-bentonites may occur in the extensional setting on the northern margin of the Yangtze Block. Hf isotopic compositions of the volcanic zircons in the K-bentonites imply that the source magmas of the K-bentonites are mainly mantle-derived, and may have mixed with the crustal materials from the northern margin of the Yangtze Block. Based on the difference in whole-rock and zircon geochemistry of the K-bentonites from Heyu and Jiuqunao, two episodes of the source volcanic eruptions of the K-bentonites could be identified. The K-bentonite at Heyu most probably represents the record of the old episode, while that at Jiuqunao represents the record of the young one. The here proposed dual episodic deposition of K-bentonites within the Doushantuo cap carbonates holds potential significance to constrain 1) the duration of the cap carbonate deposition and 2) their genesis in potential slushball or snowball Earth environments. [ABSTRACT FROM AUTHOR]

• Diverse organic-walled microfossils have been revealed from the early Neoproterozoic Qinggouzi Formation in North China. • The Great Unconformity in northeastern North China represents a major depositional gap of >200 Myr. • The Great Unconformity is widespread but diachronous in the North China Craton. The Great Unconformity at the Precambrian-Cambrian boundary has been recognized on several continents and may provide critical insights into the environmental context of the Cambrian explosion. However, the geodynamic drivers, geochronological duration, and paleogeographic extent of the Great Unconformity remain unconstrained in many cases. Recently, a major depositional gap of varying magnitudes has been reported around the Precambrian-Cambrian boundary in several regions of North China, leading to the interpretation that the Great Unconformity may have been widespread but diachronous across the North China Craton. However, the magnitude of the Great Unconformity remains unknown in northeastern North China, largely because of the poor age constraints on the thick Proterozoic–Cambrian successions in this region. Here we use biostratigraphic data to constrain the depositional age of Proterozoic strata below the Great Unconformity in northeastern North China. We report a diverse organic-walled microfossil assemblage from the Qinggouzi Formation in southern Jilin Province, northeastern margin of the North China Craton. Typical late Mesoproterozoic to early Neoproterozoic microfossils, including Trachyhystrichosphaera aimika and Proterocladus antiquus , are present in Qinggouzi assemblage, providing a solid biostratigraphic constraint on the Qinggouzi Formation. Given that the overlying Shuidong Formation contains typical early Cambrian small shelly fossils, our new data indicate that the Great Unconformity in northeastern North China represents a major depositional gap of >200 Myr. Thus, the new data, along with other available biostratigraphic and geochronological data from over the world, provide robust constraints on the paleogeographic extent, chronostratigraphic duration, and diachronous nature of the Great Unconformity. [ABSTRACT FROM AUTHOR]

The Meso-(?) and Neoproterozoic Huaibei Group in the Huaibei region, North China Craton (NCC), is emerging as a target for geobiological and tectonic studies due to its thick unmetamorphosed sediments with well-preserved organic-walled fossils. However, the lack of accurate age constraints for this sedimentary sequence dramatically hampers our ability to take full advantage of the rich geological and paleontological history recorded in the Huaibei Group. Particularly, the depositional age of the uppermost unit of the Huaibei Group, the Gouhou Formation, is a controversial issue. Although it is widely accepted that there is an unconformity between the Gouhou Formation and the overlying early Cambrian Houjiashan Formation, the magnitude of this unconformity and hence the scale of the underlying tectonic event are unconstrained due to the uncertainty of the sedimentary age for the Gouhou Formation which has been variously interpreted as Cambrian, Cryogenian–Ediacaran (∼720 Ma to ∼541 Ma), and Tonian (1000 Ma to ∼720 Ma). To improve our knowledge about this sedimentary gap, we carried out a biostratigraphic study of the Gouhou Formation. Our investigation using a low manipulation maceration technique revealed a diverse organic-walled microfossil assemblage. A total of 22 taxa have been revealed, including a new species— Dictyosphaera tacita n. sp. Importantly, the co-occurrence of Trachyhystrichosphaera , Valeria , and Dictyosphaera in the Gouhou Formation suggests a likely Tonian age. The biostratigraphic data indicate an infra-Cambrian depositional gap of >200 myr between the Tonian Gouhou Formation and Cambrian Houjiashan Formation, perhaps driven by a major tectonostratigraphic event. [ABSTRACT FROM AUTHOR]

• Xenotime and monazite are documented from the Xuhuai Group. • Authigenic xenotime and monazite gave Pb-Pb ages of ca. 919 Ma to ca. 1086 Ma. • New ages suggest evolution and diversification of eukaryotes at ca. 1.0 Ga. • New ages confirm the use of Trachyhystrichosphaera aimika as an index fossil. Meso-Neoproterozoic sedimentary successions in the southeastern margin of North China Craton contain a wealth of fossil and chemostratigraphic information, which aids in our understanding of early multicellular life and environment coevolution. However, a lack of reliable age constraints means the timing of these fossil occurrences and the corresponding evolutionary tempo of multicellular life remain disputed. This study aims to provide new age constraints by means of authigenic xenotime and monazite geochronology, coupled with morphological observation and mineral chemical analyses. Morphological observation and mineral chemistry allows differentiation of authigenic xenotime and monazite from detrital origins. Authigenic xenotime from the Shijia Formation, upper part of Meso-Neoproterozoic sedimentary successions, gave a SIMS Pb-Pb age of 919 ± 23 Ma, whereas authigenic monazite from the Xinxing and Liulaobei formations, lower part of Meso-Neoproterozoic sedimentary successions, produced SIMS Pb-Pb ages of 1086 ± 17 Ma and 1086 ± 120 Ma, respectively, all of which are interpreted as minimum depositional ages. The new ages suggest the crown group multicellular eukaryotes have highly evolved and diversified prior to 1.0 Ga, and confirm the use of Trachyhystrichosphaera aimika as an index fossil for the Mesoproterozoic-Neoproterozoic transitional period. [ABSTRACT FROM AUTHOR]

Highlights: [•] Lamina-by-lamina pyrite framboid measurements were conducted for Lantian black shales. [•] The Ediacaran Lantian black shales were deposited in fluctuant redox conditions. [•] The frequent redox condition changes are not clearly indicated by RSTE data. [ABSTRACT FROM AUTHOR]

Highlights: [•] Organic-walled microfossils from the early Neoproterozoic Liulaobei Fm., N. China. [•] Previous suggestion of a Cryogenian-Ediacaran age for Liulaobei Fm. is questioned. [•] Trachyhystrichosphaera aimika is a useful early Neoproterozoic index fossil. [ABSTRACT FROM AUTHOR]

• We report the structural characteristics of Proterozoic organic-walled microfossils using Raman spectroscopy in North China. • CM in Ruyang and Liulaobei microfossils experienced low-grade metamorphism with apparent peak metamorphic temperatures of ~200 °C. • Heterogeneities in structural characteristics exist among different subcellular structures of S. macroreticulatum and different taxa of the same stratigraphic horizon. Raman spectroscopy is a minimally intrusive and minimally destructive technique that has played an important role in analyzing Precambrian carbonaceous microfossils and microstructures. Previous studies have shown that heterogeneities in structural order of carbonaceous material (CM) as revealed by Raman spectroscopy can be preserved in Proterozoic silicified cyanobacterial fossils. However, such heterogeneities have not been documented in Proterozoic eukaryotic microfossils preserved as carbonaceous compressions. In this study, we used Raman spectroscopy to investigate the structural characteristics of organic-walled microfossils, including eukaryotes preserved as carbonaceous compressions, from the late Paleoproterozoic Ruyang Group and the early Neoproterozoic (Tonian) Liulaobei Formation in the North China Craton. Raman geothermometers indicate that CM experienced low-grade metamorphism with apparent peak metamorphic temperatures of ~200 °C for both the Ruyang and Liulaobei microfossils. Heterogeneities in structural characteristics of CM in eukaryotic microfossils were found among different subcellular structures of Shuiyousphaeridium macroreticulatum and among different taxa from the same stratigraphic horizon. We suggest that these heterogeneities can be attributed to differences in precursor organic compounds; thus, the importance of organic precursors should be considered in CM Raman geothermometry studies, especially in environments where heating events occurred quickly. The Raman data presented here are also consistent with hypotheses that the Ruyang microfossils Dictyosphaera delicata and S. macroreticulatum are biologically conspecific taxa with their vesicle walls having similar CM Raman features, and that the Liulaobei microfossils Leiosphaeridia jacutica and L. tenuissima are distinct taxa despite their similarities in morphologies other than vesicle wall thickness. Although more data are needed to verify the consistency of interspecies, intraspecies, and intraspecimen variability, this study indicates that Raman spectroscopy may have the potential to provide an independent test of early eukaryote taxonomy, which has been traditionally based only on morphological features, and to reveal heterogeneities of CM of early eukaryotic organisms. [ABSTRACT FROM AUTHOR]